SpaceX Is Building Starship from Stainless Steel
In January, SpaceX CEO Elon Musk tweeted that the launch system Starship-Super Heavy, previously named the BFR (Big Falcon Rocket), would be built of stainless steel rather than carbon fiber or aluminum. Starship is the spaceship, the upper stage, and Super Heavy is the rocket booster. The spacecraft’s purpose is to simultaneously seat 100 passengers and deliver more than 100 tons of cargo to the Moon and Mars and for traveling to deep space. SpaceX plans to use high-quality 301 brand stainless steel. However, experts say that Starship nothing more but a demonstration rocket that will never fly, and that’s why it can be made from anything, even wood.
According to Musk, the main reason for building a rocket from stainless steel is the short construction time. Construction of carbon fiber or aluminium would be lighter in weight, but development will take more time. Time is of essence for SpaceX because of the company’s plans of building a self-sufficient city on Mars by 2050. According to the scientific director of the Institute of Space Policy, Ivan Moiseev, the main advantage of stainless steel is that it is inexpensive.
“When engineers choose a material for the construction of a rocket, many parameters are taken into account: firstly, strength and specific gravity are very important. As for the Starship spacecraft, the main parameter of choice here is the low cost of stainless steel. Moreover, because SpaceX is building a rocket in open air, it will fare better than the spaceship from ordinary tin, which will rust,” Ivan Moiseev told Asgardia Space News.
Currently, the cost per kilogram of sheet steel is total about $3. And there are a lot of enterprises that produce stainless steel, so scarcity is not an issue. On the other hand, the cost per kilogram of carbon fiber is about $135. Because of its specific properties, the scrap rate per kilogram is about 35%, which means the price per kilogram will be higher, approximately $200.
Another benefit of stainless steel is its resilience to temperature changes. Fuels for rockets has extremely low temperature, so the material of tanks should be able to withstand it. Ordinary steel under the conditions of operation of space transport can crack, which then cannot be repaired. However, nickel-chromium alloys are not as fragile as other steel grades and are resistant to ultra low temperatures. Microcracks in the material will not form, potentially preventing rocket failures.
Musk plans to replace heat-resistant tiles that are now being used to protect the hull of space ships with a reusable stainless steel heat shield. Reducing the weight of the launch system is key to averting the risk of a damaged or lost tile jeopardizing the heat shield. The hull will consist of two layers of steel, like a double-layered steel “sandwich.” By comparison, for using carbon, 60 to 120 layers would be required. To protect the ship from high temperatures, water or fuel that flow into the space between the layers will then be expelled through the microperforations in its steel plate.
Stainless steel has a high melting point — about 1,500 degrees Fahrenheit (800 degrees Celsius). This figure is much higher than that of aluminum and carbon, which begin to deform already at a temperature of 300 degrees Fahrenheit (150 Celsius). Therefore, the spaceship will be protected from many potential risks faced by modern rockets made of aluminum and carbon.
Ivan Moiseev noted that the Starship is not designed for flight, but only for reaching an altitude of a mere 500 meters, and that is why it is possible to consider any options for its construction, provided that the engine thrust exceeds the mass of the rocket itself.
“Theoretically, the option of the ‘sweating screen’ was considered, when the cooling of the case occurs due to the removal of liquid, which evaporates and takes heat with it. But in practice, no one tried to realize this, because with such a scenario, the building of a rocket is more complicated than the known scenarios,” he told.
However, Musk plans to using the Starship-Super Heavy system for cargo delivery to the Moon and Mars, as well as for building a self-sufficient city on the red planet by 2050. He has claimed that the cost of ticket to Mars should be cheap and returning to Earth should be free-of-charge.
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